Phase Transformation Of Zirconia Research Articles

Effect of Hydrothermal, Chemical, and Mechanical Degradation on Flexural Strength and Phase Transformation of Ground, Glazed, and Polished Zirconia

Objectives: Evaluation of the effect of grinding on flexural strength of zirconia after low temperature degradation (LTD) and pH-cycling. Materials and Methods: Sixty-four bar-shaped specimens of yttria-stabilized tetragonal polycrystalline zirconia were milled, sintered, wet-polished, and divided into 8 groups (N=8). The four control groups were not aged while artificial aging was performed in the 4 experimental groups in three steps including LTD in steam for 40h, pH-cycling, and tooth brushing for artificial aging. All groups underwent surface preparations as follows: standard polishing without surface treatment (Sp), grinding with a blue-yellow band diamond instrument (Gr); grinding with a diamond rotary instrument (DRI) and then over-glazing (Gl); grinding with a DRI followed by two-step intraoral polishing (Po); standard polishing and aging (Sp-Ag); grinding and aging (Gr-Ag), grinding, over-glazing and aging (Gl-Ag); and grinding, polishing and aging (Po-Ag). Monoclinic content was assessed in one specimen of each group by X-ray diffraction (XRD). The 3-point flexural strength test was performed in a universal testing machine. The results were analyzed with two-way ANOVA and Tukey’s test (α=0.05). Results: Mean flexural strength (Mpa) was significantly higher in groups Gr and Po compared to group Sp (both, P<0.0001) and group Gl (both, P<0.0001). In XRD analyses, the highest monoclinic phase before aging was observed in group Gr (12.6%), and after aging in group Gr-Ag (51.2%). Conclusion: Grinding and polishing increased the flexural strength, while glazing did not exhibit any significant effect on this parameter. Furthermore, aging did not adversely affect flexural strength.

Microstructure of Stress‐Induced Martensite in Micron‐Sized Zirconia Single Crystal Spheres

Martensitic phase transformation of zirconia (ZrO2), when realized from the superelastic effect, has immense potential in energy applications, such as micro‐actuation and high‐energy dissipation/damping. In this study, martensitic transformation in ZrO2 is studied using a newly developed microscale phase field model, which is scale‐independent and contains an averaged gradient term. The model is implemented using the FEniCS package in Python. With a thorough explanation of the model construction, the mechanics of phase transformation are detailed, and the material behaviors under different stress conditions are discussed. Mesh sensitivity, multivariant evolution, and the effect of particle size are analyzed to understand the martensite evolution in superelastic ZrO2. This work provides new insight into the martensitic phase transformation behaviors of micron‐sized spherical ZrO2 particles.

A thermogravimetric comparative study of the high temperature steam oxidation of bare and pre-oxidized Zircaloy-4, M5Framatome and Optimized ZIRLO™

For Loss of Coolant Accident (LOCA) analysis, high-temperature oxidation kinetics in steam of Zircaloy-4 and the two Nb-bearing alloys used in French Pressurized Water Reactors (PWRs), M5Framatome11M5 and M5Framatome are trademarks or registered trademarks of Framatome or its affiliates, in the USA or other countries. and Optimized ZIRLO™22Optimized ZIRLO is a trademark or registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiaries in the United States and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners., have been studied using Thermo-Gravimetric Analysis (TGA) technique in the temperature range of 900–1200 °C. A specific test procedure allowing the use of a high steam flow rate and good steam supply to the whole specimen surface, as well as fast heating of the specimen, has been developed. Clean kinetic data, not affected by steam starvation, were obtained on the bare, as-received alloys. For as-received claddings, oxidation kinetics are comparable and close to parabolic for the three alloys at 1100 °C and above. Below 1100 °C, a significant deviation from the parabolic kinetic regime was observed, and M5 Framatome oxidizes slower than Zircaloy-4 and Optimized ZIRLO. Thanks to the fast-heating protocol, the influence of pre-oxidation, simulating corrosion in normal reactor operation, could be investigated, avoiding evolution of the pre-oxidation scale during a slow, long heating phase. Pre-oxidized Zircaloy-4 and M5 Framatome were investigated. A strong protective effect is observed below 1200 °C, while at 1200 °C, the pre-oxidation layer appears to be much less protective, possibly due to the monoclinic to tetragonal zirconia phase transformation.

Novel oxide based anti-corrosion composite coating for gas turbines

In the present study glass-ceramic−8YSZ based multilayered functionally graded corrosion resistant coating was developed for gas turbine applications. Corrosion resistance property of developed coating was evaluated by exposing coating to molten mixture of 80 wt% Na2SO4 + 20 wt% NaCl in air at 1000 °C up to 100 h. It was found that coating morphology was gradually changed with respect to time at 1000 °C. No thermally grown oxide (TGO) layer was observed within different layers of TBC. However, thin reaction film was developed at substrate-coating interface, which helped to increase adherence of coating with substrate. Tetragonal zirconia to monoclinic zirconia phase transformation was not occurred in top coat even after long corrosive salt attack that strengthened TBC system. Developed coating showed good potential to be used as corrosion resistant coating for actual superalloy based gas turbine engine components.

Surface property changes observed in zirconia during etching with high-concentration hydrofluoric acid over various immersion times.

This study investigated the degree of phase transformation, surface roughness, and bond strength of zirconia immersed for various times in a 40% hydrofluoric acid (HF) solution. Non-etched sintered zirconia specimens were used as the control, while experimental groups were etched with a 40% HF solution for 5, 10, 20, 40, 80, 160 and 320 min. In each of the control and experimental groups, five specimens for X-ray diffraction analysis, four for surface morphology and surface roughness analysis, and ten for bonding strength measurement were used. As a result, the surface roughness of zirconia increased as the application time increased during the 40% HF etching, but the bond strength between zirconia and resin cement did not increase proportionally. The phase transformation from tetragonal to monoclinic also gradually increased with application time.

Effect of sintering programs and surface treatments on monolithic zirconia.

To investigate the effect of sintering programs and surface treatments on surface properties, phase transformation and flexural strength of monolithic zirconia. Zirconia specimens were sintered using three distinct sintering programs [classic (C), speed (S), and superspeed (SS)] (n = 56, each). One sample from each group underwent scanning electron microscopy (SEM) and grain size analysis following sintering. Remaining samples were divided into five subgroups (n = 11) based on the surface treatments: control (CL), polish (P), glaze (G), grind + polish (GP), and grind + glaze (GG). One sample from each subgroup underwent SEM analysis. Remaining samples were thermally aged. Monoclinic phase volume, surface roughness, and three-point flexural strength were measured. Monoclinic phase volume and surface roughness were analyzed by Kruskal-Wallis and Dunn tests. Flexural strength was analyzed by two-way ANOVA and Weibull analysis. The relationships among the groups were analyzed using Spearman's correlation analysis. Sintering program, surface treatment, and sintering × surface treatment (P ≤ .010) affected the monoclinic phase volume, whereas the type of surface treatment and sintering × surface treatment affected the surface roughness (P < .001). Type of sintering program or surface treatment did not affect the flexural strength. Weibull analysis revealed no significant differences between the m and σo values. Monoclinic phase volume was positively correlated with surface roughness in the SGG and SSP groups. After sintering monolithic zirconia in each of the three sintering programs, each of the surface treatments can be used. However, for surface quality and aging resistance, G or GG can be recommended as a surface finishing method.

Evaluation of Feasibility on Dental Zirconia-Accelerated Aging Test by Chemical Immersion Method.

The aim of this study was to investigate the low-temperature degradation (LTD) kinetics of tetragonal zirconia with 3 mol% yttria (3Y-TZP) dental ceramic using two degradation methods: hydrothermal degradation and immersed degradation. To study transformation kinetics, we prepared 3Y-TZP powders. We pressed these powders uniaxially into a stainless mold at 100 MPa. We then sintered the compacted bodies at intervals of 50 °C between 1300 °C and 1550 °C and immersed the specimens at various temperatures from 60 °C to 80 °C in 4% acetic acid or from 110 °C to 140 °C for the hydrothermal method. We used a scanning electron microscope (SEM) to confirm crystalline grain size and used X-ray diffraction to analyze the zirconia phase. As the sintering temperature increased, the calculated crystalline grain size also increased. We confirmed this change with the SEM image. The higher sintering temperatures were associated with more phase transformation. According to the Mehl-Avrami-Johnson equation, the activation energies achieved using the hydrothermal method were 101 kJ/mol, 95 kJ/mol, and 86 kJ/mol at sintering temperatures of 1450 °C, 1500 °C, and 1550 °C, respectively. In addition, the activation energies of the specimens immersed in 4% acetic acid were 60 kJ/mol, 55 kJ/mol, 48 kJ/mol, and 35 kJ/mol, with sintered temperatures of 1400 °C, 1450 °C, 1500 °C, and 1550 °C, respectively. The results showed that a lower sintering temperature would restrain the phase transformation of zirconia because of the smaller crystalline grain size. As a result, the rate of LTD decreased.

Surface and interfacial microstructure evolution of isothermally oxidized thermal barrier coating system

Novel multilayer functionally graded thermal barrier coating (TBC) system consisting of a newly developed glass-ceramic based bond coating, glass-ceramic-25% yttria stabilized zirconia (YSZ) composite coating and 100% 8-YSZ top coating. Since TBC is a layered system property matching between each layer is a major concern. Therefore, thermal properties of the developed glass-ceramic coating and composite coating were studied in detail. The developed system was exposed to static oxidation at 1100 °C for 100 h. To assess the efficacy of the TBC system, XRD phase analysis and also mechanical properties like Young's modulus and nanohardness was performed at each layer for both before and after isothermal oxidation. From the surface and interfacial microstructure evolution it was observed that there was crack development at composite coating-top coating interface, which was due to zirconia phase transformation from tetragonal to monoclinic crystal structure, confirmed by the presence of monoclinic zirconia XRD diffraction peaks in XRD analysis. Additionally, Raman spectroscopy was also carried out on the isothermally oxidized specimen, which also pointed out the presence of monoclinic crystal structure. Even though developed TBC system failed to protect the nimonic alloy (AE435) substrate from thermal exposure at 1100 °C for 100 h the glass-ceramic/substrate had a good interfacial adhesion. Main advantage of using glass-ceramic coating is its ability to tune coating properties by changing the composition. Thus, future works are being carried out to alter the glass-ceramic composition to develop a potential TBC system.

A phase transformation–phosphorescence model of europium-doped yttria-stabilized zirconia and its application in two-dimensional thermal history measurement

Phosphorescence thermal history sensors are off-line temperature measurement devices with potential applications in harsh environments. However, changes in phosphorescence after heating at various temperatures or for various durations cannot be precisely quantified based on current theory. In this study, europium-doped yttria-stabilized zirconia (YSZ:Eu) was selected as a potential thermal history sensor and its structural and phosphorescence properties were characterized after heating at various temperatures. It was found that the tetragonal-to-cubic phase transformation of zirconia had a major effect on the phosphorescence intensity ratio (PIR) of YSZ:Eu. Accordingly, theoretical and semi-empirical versions of a novel phase transformation–phosphorescence model were developed based on Judd–Ofelt theory and the Avrami equation, and were used to quantify phosphorescence changes induced by heating YSZ:Eu at various temperatures and for various durations. The results of a calibration experiment showed that the PIR increased from 0.5 to 1.0 as the heating temperature and heating duration increased from 900 °C to 1200 °C and from 10 min to 80 min, respectively. The mean relative fitting errors of the theoretical and semi-empirical model were 2.2 % and 5.6 %, respectively. Finally, thermal history measurement was demonstrated in a flame-impingement experiment that was conducted using a phosphor-coated plate subjected to two different heating durations. The phosphorescence signals collected by an industrial camera were processed to yield two-dimensional (2D) surface-temperature distributions of the plate and compared with those obtained using an infrared camera. The average differences between the 2D surface-temperature distributions obtained by the two methods were 5.9 °C and 6.5 °C for 40 min and 80 min heating durations, respectively. These findings enhance theoretical understanding of thermal history sensing and will facilitate advancement from single-point to 2D thermal history measurement.

Improving Bond Strength of Translucent Zirconia Through Surface Treatment With SiO2-ZrO2 Coatings.

Translucent monolithic zirconia ceramics have been applied in dental clinics due to their esthetic translucent formulations and mechanical properties. Considering inherent ceramic brittleness, adhesive bonding with resin composite increases the fracture resistance of ceramic restorations. However, zirconia is a chemically stable material that is difficult to adhesively bond with resin. To investigate the influences of SiO2-ZrO2 coatings on adhesive bonding of zirconia and the surface characterization of those coatings. Translucent zirconia discs were classified into groups based on surface treatments: CT (control), SB (sandblasting), C21(SiO2:ZrO2=2:1), C11(SiO2:ZrO2=1:1), and C12 (SiO2:ZrO2=1:2) (n=10). Surface characterization of coatings on zirconia were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), surface roughness assessment (Ra), X-ray diffraction (XRD), water contact angle (WCA), translucency parameter (TP), and shear bond strength (SBS). Two-way ANOVA for shear bond strength results and ANOVA for Ra and WCA were performed. SEM images revealed SiO2 islands on zirconia disks coated with SiO2-ZrO2. Surface roughness of C12, C11, and C21 groups was significantly larger than those of groups SB and CT (p<0.05). XRD results showed that phase transformation of zirconia disks was detected only in the SB group. In addition, SiO2-ZrO2 coatings reduced WCA. The translucency decreased only in group C21. Group C11 showed the highest shear bond strength under both aging conditions. SiO2-ZrO2 coating is a promising method to enhance the adhesive resin bonding of translucent zirconia without causing phase transformation of translucent zirconia.

Influence of shading on zirconia's phase transformation and flexural strength after artificial aging.

The aim of this study was to determine the phase transformation and the influence of aging on the flexural strength of different colored zirconia. The effect of hydrothermal aging in an autoclave was compared with the effect of mechanical stress by simulating chewing. High-strength zirconia (3Y-TZP) was investigated in three different colors: uncolored, A3, and D3. Disc-shaped specimens (N=3) were analyzed by X-ray diffraction (XRD), and flexural strength was determined on bar-shaped specimens (N=15) in a 4-point bending test before and after performing two different aging protocols: aging in an autoclave (134°C, 70h) and aging in a chewing simulator (5kg load, 1.2 million cycles). During autoclave aging, the fraction of monoclinic phase on the surface was determined every 5h. Once this exceeded 25vol%, aging of the bar specimens was stopped. While in the unstained group the mean value of the proportion of monoclinic phase already exceeded 25vol% after 30h in the autoclave, this was the case in both stained groups only after 70h. No measurable phase transformation could be detected after chewing simulation. Only color A3 showed a statistically significant (p≤0.05) decrease in flexural strength after aging in the chewing simulator. The colored zirconia showed a higher resistance to phase transformation through hydrothermal aging. The metal oxides in the staining solutions are assumed to hinder the phase transformation in the zirconia. Therefore, the significant reduction in the stained zirconia after chewing simulation is particularly interesting.

Is Ammonium Hydrogen Difluoride a Solution for Zirconia Surface Conditioning?

This research investigated the topographical features and phase transformation of high-translucent monolithic zirconia after different surface conditioning methods. Zirconia slabs were divided into six groups according to surface treatment method. Group I: etched with hydrofluoric acid (HF); Group II: etched with an experimental acid solution (EAS); Group III: melt-etched with ammonium hydrogen difluoride (AHD); Group IV: air abrasion (AB); Group V: etched with EAS after air abrasion (AB+EAS); Group VI: melt-etched with AHD after air abrasion (AB+AHD). Surface topographies of specimens were documented by scanning electron microscopy (SEM). Tetragonal-to-monoclinic phase transformation was detected by X-ray diffraction and surface evaluation of zirconia specimens; surface roughness and contact angle measurements were performed. The data were statistically analyzed by the Kruskal- Wallis test and post hoc tests (P⟨0.05). The acid-etched zirconia groups (Group I, II, and III) showed the lowest contact angle and surface roughness values (P⟨0.05), while the air abrasion groups (Group IV, V, VI) showed the highest. The SEM images also supported these results. Within the limitations of this in vitro study, treating the monolithic zirconia surfaces with EAS or AHD after air abrasion may be recommended to alter the zirconia surfaces.

Enhancing the toughness of nano-composite coating for light alloys by the plastic phase transformation of zirconia

Toughness of ceramic coatings is essential for engineering deploys of light alloys, especially for the scenarios tackling with corrosion and wear. This work reports a toughened ZrO2/MgO coating on Mg alloy enabled by stress-induced martensite transformation from tetragonal zirconia (t-ZrO2) to monoclinic zirconia (m-ZrO2), which is achieved by the plasma electrolytic oxidation (PEO) process. Observations reveal that the interfaces between ZrO2 and MgO grains are essential in inducing phase transition during the toughening process. Interestingly, semi-coherent interfaces were found between t-ZrO2 and MgO, and the mismatched atoms at the interface cause local lattice distortions. These lattice distortions provide an appropriate dislocation density (2.2 × 105 /m2–4.1 × 105 /m2), which not only ensures the stability of the interface but also provides a stress transfer channel to induce martensite transformation of ZrO2. The plastic phase transformation is accompanied with volume expansion of ZrO2 grains, thus a compressive stress field is generated to resist the crack propagation with an enhancement of the plasticity of the composite ceramics. As a result, the toughness of the enhanced coating is about 1.15 times higher than that of the traditional PEO coating. This work provides an alternative strategy for designing toughened ceramic coatings for light alloys.

The enhanced shear bond strength of resin cement to zirconia with ordered conical spots through the CO2 laser process.

In this study, a new shear bonding system was created that uses a CO2 laser to form a pattern of conical spots on a zirconia prosthesis surface to improve mechanical interlocking. Four types of zirconia substrates were employed, which underwent particle abrasion after being polished, machined, spotted, and spot-particle abraded. The surface roughness of each substrate was measured via scanning electron microscopy and X-ray diffraction (XRD). A shear bond strength test was performed with the zirconia-based material and a composite resin assuming abutment construction. XRD did not indicate that forming spots caused a phase transformation in zirconia with respect to machined zirconia. The shear bond strength was approximately twice that of the machined samples and approximately 2.3 times that of the samples that underwent particle and spot-particle abrasion. Surface modification by spotting improved the mechanical fitting force. However, no significant difference was observed between particle abrasion and spot-particle abrasion.

Effect of nonthermal argon plasma treatment on the surface properties and phase transformation of zirconia.

This study aims to evaluate the effect of applying different parameters of nonthermal argon plasma (NTAP) on the surface roughness and phase transformation of yttrium-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics. A total of 60 zirconia samples were prepared and randomly divided into six groups according to their surface treatments (n = 10). Group 1: control group; Group 2: argon plasma with a flow rate of 5 lt/min for 4 min; Group 3: 8 lt/min for 4 min; Group 4: 8 lt/min for 2 min; Group 5: 5 l/min for 2 min; Group 6: air abrasion with Al2O3 particle. The surface roughness was measured with a profilometer, and surface topography was observed using scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was performed to investigate the phase transformation. The air abrasion group showed the highest surface roughness. The lowest relative monoclinic phase amount (Xm) was observed in the control group (0.4%), and the highest Xm value was observed in group 6 (7.8%). While the air abrasion group showed the highest average surface roughness, it also caused the highest phase transformation. With a flow rate of 8 lt/min for 2 min NTAP treatment increased the surface roughness without causing significant phase transformation.

Influence of loading and aging on the fracture strength of an injection-molded two-piece zirconia implant restored with a zirconia abutment.

To investigate the fracture strength and potential phase transformation of an injection-molded two-piece zirconia implant restored with a zirconia abutment after loading and/or aging. Thirty-two two-piece zirconia implants (4.0 mm diameter) restored with zirconia abutments were embedded according to ISO 14801 and divided into four groups (n=8/group): Three groups were either exclusively hydrothermally treated (group HT; 85°C), dynamically loaded (group DL; 107 cycles; 98 N), or subjected to both treatments simultaneously (group DL/HT). One group remained untreated (group 0). A sample from each group was cross-sectioned and examined by scanning electron microscopy for possible crystal phase transformation. The remaining samples were then loaded to fracture in a static loading test. A one-way ANOVA was used for statistical analyses. During dynamic loading, three implants of group DL and six implants of group DL/HT fractured at a load of 98 N. The fracture strength of group DL/HT (108± 141 Ncm) was significantly reduced compared to the other groups (group 0: 342± 36 Ncm; HT: 363 ± 49 Ncm; DL: 264 ± 198 Ncm) (p < .05). Fractures from group 0 and HT occurred at both implant and abutment level, whereas implants from group DL and DL/HT fractured only at implant level. A shallow monoclinic transformation zone of approximately 2μm was observed following hydrothermal treatment. Within the limitations of this study, it can be concluded that dynamic loading and the combination of loading and aging reduced the fracture strength of the implant abutment combination. Hydrothermal treatment caused a shallow transformation zone which had no influence on the fracture strength.

Structure and fracture behavior of ion-beam-modified SiC-Al2O3-ZrO2 ceramic composites

SiC-Al2O3-ZrO2 ceramic composite with heterointerfaces was prepared by hot pressing and irradiated with 1.2 MeV Si ions at room temperatures. The microstructural evolution and mechanical properties were investigated. The results showed that the phase transformation of zirconia revealed by GIXRD and TEM are associated with the accumulation of oxygen vacancies clusters originated by damage and the size of displacement cascades. Complete amorphization of SiC particles were observed at 5.5 dpa, and developed into collection band at 55 dpa due to the mixture of point defect clusters and extend defects at high damage level. The nanohardness and elastic modulus irradiation decreased with increasing of damage level. The fracture behavior of materials and relative mechanism under ion irradiation were discussed.

Effects of argon plasma and aging on the mechanical properties and phase transformation of 3Y-TZP zirconia.

To evaluate the flexural strength (FS) and flexural modulus (FM) of a commercial 3Y-TZ0P ceramic after artificial aging and either without or with two application times of non-thermal plasma treatments (NTP). In addition, changes in crystalline phase transformation and surface nano-topography after NTP application, during different aging periods, were evaluated. Ninety 3Y-TZP bars (45x4x3 mm) were made for FS and FM testing, and assigned to nine groups (n=10): no NTP/no aging (Control); no NTP/4h aging; no NTP/30h aging; 10s NTP/no aging; 10s NTP/4h aging; 10s NTP/30h aging; 60s NTP/no aging; 60s NTP/4h aging and 60s NTP/30h aging. Artificial accelerated aging was simulated using an autoclave (134º C at 2 bar) for up to 30h. FS and FM were assessed using a universal testing machine and data analyzed using a ANOVA and Tukey test (α=0.05). The volume change in zirconia monoclinic phase (MPV) was evaluated using X-ray diffraction and surface nano-topography was assessed using atomic force microscopy (baseline until 30h-aging). NTP application did not influence the FS and FM of zirconia. Compared to the Control (no NTP/no aging), the FS of zirconia samples treated for 30 hours in autoclave ("no NTP/30h aging" group) increased. Artificial aging for 30 hours significantly increased the FM of zirconia, regardless of NTP application. MPV tended to increase following the increase in aging time, which might result in the surface irregularities observed at 30h-aging. NTP did not alter the zirconia properties tested, but 30h-aging can change the zirconia FS, FM and MPV.

Prolonged flash sintering and its effects on defect chemistry, phase transformation and ionic conductivity of yttria-stabilized zirconia

Prolonged flash sintering and its effects on defect chemistry, phase transformation and ionic conductivity of yttria-stabilized zirconia

Comparative effects of tungsten, diamond burs and laser for residual adhesive removal after orthodontic debonding on flexural strength, surface roughness and phase transformation of high-translucent zirconia: An in vitro study

ObjectivesInformation regarding the effects of orthodontic bracket debonding on zirconia restorations, and the preferred method for residual adhesive removal from the zirconia restoration surface is lacking. Thus, this study aimed to assess the effects of different methods of residual adhesive removal after orthodontic bracket debonding on flexural strength, surface roughness, and phase transformation of high-translucent (HT) zirconia. Materials and methodsThis in vitro study evaluated 72 bar-shaped HT zirconia specimens; 18 specimens were assigned to the control group. Metal brackets were bonded to the remaining specimens by resin cement. After bracket debonding, the residual adhesive on the surface of specimens was removed by three methods (n=18): a 30-flute tungsten-carbide (TC) bur at low speed, an ultrafine diamond bur at high speed, and Er:YAG laser irradiation. The surface roughness (Ra and Rz) was measured. X-ray diffraction (XRD) analysis was carried out, and the flexural strength was measured as well. Data were statistically analyzed (α=0.05). ResultsBefore polishing, all methods increased the Ra and Rz values (P<0.05) except for the diamond bur yielding a Rz value comparable to that of the control group. The Ra values of the test groups were comparable after polishing, and still higher than that of the control group (P<0.05). The flexural strength of all three test groups was comparable (P>0.05), and significantly lower than that of the control group (P<0.001). The monoclinic phase was not observed in any group. ConclusionsOrthodontic bracket debonding adversely affects the surface roughness and flexural strength of zirconia despite polishing.